This invention relates to display apparatuses which have light emitting elements arranged in a matrix form on a printed substrate so that the light emitting elements are individually turned on and off to display images such as characters, and more particularly to display apparatuses which is adapted to dissipate heat developed by electronic components such as light emitting elements mounted on a printed board.
Conventionally, there have been utilized display apparatuses involving information display boards installed at railway stations or public squares as well as inside displays provided in vehicular rooms. These display apparatuses have light emitting elements such as light emitting diodes (hereinafter referred to as LEDs) in a matrix form so that the LEDs are individually controlled of emission of light to display characters and so on for displaying information of news, time, temperature, etc. The display apparatus of this kind has a structure for example as shown in FIG. 4
In FIG. 4, 1 is a printed board formed of a glass-epoxy resin or the like having interconnect patterns on opposite surfaces. The printed board 1 has chip LEDs 2 matrix-arranged on one surface and IC components (controlling components) 3 matrix-arranged on the other surface. The IC components comprise controlling and driving components for selectively turning on and off the LEDs 2 on the opposite side. 4 is a metal fixture for fixing the display apparatus on an assembly on which the display apparatus is installed without being interfered by the IC components. The display apparatus is mounted on a housing, etc., of such an assembly by fastening screws in attachment holes 4a.
The printed board 1 on which LEDs 2 and IC components 3 are thus mounted is formed by an electrically insulative substrate such as a glass-epoxy resin substrate formed with interconnect patterns on the surfaces thereof. To mount LEDs and IC components on the printed board 1, surface mounting is usually adopted wherein these parts are rested on a surface of the printed board 1 to directly solder lead wires or electrode terminals of these parts onto the interconnect pattern on the printed board 1. In such cases, the connection between LEDs 2 and IC components 3 is carried out via through-holes formed in the printed board 1 or by way of lateral faces of the printed board 1.
The technique of mounting electronic components on a electrically insulative printed board for electronic assemblies is being applied to various electronic devices and apparatuses. In recent, the surface mounting that electronic components are directly soldered on the surface of a printed board is becoming a main stream in the field of mounting electronic devices and apparatuses.
Where electronic components are mounted on a electrically insulative printed board, there is almost no problem for small consumption power of electronic components. On the contrary, where mounting with LEDs for large-sized displays as stated hereinbefore or a number of heat-dissipating electronic components such as high-power semiconductor devices, the heat generated from the components is difficult to dissipate outside because of poor heat conductivity of such an electrically insulative printed board. The remaining heat is accumulated in the insulative substrate to thereby raise the temperature of electronic components, badly influencing electrical characteristics of the display apparatus. To avoid this, there is necessity of reducing the operating power low to suppress heat development, making difficult to provide a sufficient level of brightness of light.